white.] ANNOTATED CATALOGUE. 37 



Moreover, the majority of the genera, and many of the subordinate divis- 

 ions of those genera, possess no recognizable variation from those under 

 which we are accustomed to range the living species. We have, how- 

 ever, seen that a small number of those subordinate types among the 

 Conch ifers have become extinct; and we shall see that still more of them 

 among the Gasteropoda, together with a few of that class that we regard 

 as full genera, have also become extinct; but yet the fact remains that 

 these ancient non-marine mollusca, as a whole, are wonderfully like 

 their living representatives.* 



GASTEROPODA. 



Although, in zoological rank, the gasteropoda are so much in advance 

 of the Conchifera, the various families of the former seem to have been 

 developed as early in geological time as those of the latter; and so far 

 as we are now acquainted with the history of the fossil non-marine 

 mollusca of North America, it appears that highly organized laud pul- 

 monate gasteropods were introduced quite as early as any of the 

 Conchifers. Indeed, from present indications, we are led to believe that 

 the relations of the different classes of non-marine mollusca to each 

 other were much the same in all geological epochs as they are to-day. 



AURICULIDiE. 



Three or four species of gasteropods have been discovered in the 

 Cretaceous estuary deposits, and those of Bear River, Laramie series, 

 which are regarded as belonging to the family AuriculidaB ; and these 

 are the only members of that family which have been discovered in 

 North American strata, and the only ones that come within the scope 

 of this article. 



One of these species was discovered by Mr. Meek in the Cretaceous 

 estuary deposit at Coalville, Utah,t which has already been mentioned 



* There have been found in the Laramie Group two Oonchifers and one Gasteropod 

 which, so far as is now known, have living allies only in rnaxine waters, and they are 

 therefore not enumerated in this article, although they seem to have survived in the 

 brackish water Laramie Sea from the time when it was an open sea of marine saltness. 

 They are respectively Naculana inelara, Axinaa holmesiana and Odontobasis buccinoides 

 White. With these exceptions, all the known molluscan species of the Laramie Group 

 are such as we should naturally refer to some non-marine habitat. It is not at all im- 

 probable that these species of genera which are usually characteristic of open-sea waters 

 survived the land-locking of the Laramie Sea, and did not yield up their existence 

 until the complete freshening of the waters took place, when their associates Corbicula, 

 Corbula, Neritina, &c, also ceased to exist. The species which was described by me 

 as Odontobasis f formosa probably belongs to some genus of the Ceriphasiida;. For 

 remarks upon the species referred to in this note, with descriptions and figures, see An. 

 Rep. U. S. Geo). Sur. Terr, for 1878, Part I, pp. 59, 60, 102, and 103 ; plates 20, 25, and 28. 



t An. Rep. U. S. Geol. Sur. Terr, for 1878, Part I, p. 23, pi. 12, fig. 11. 



